The secondary header above is an h2 element, which may be used for any form of important page-level header. More than one may be used per page. Consider using an h2 unless you need a header level of less importance, or as a sub-header to an existing h2 element. Any header level may include links, as depicted in the example.

Third-Level Header

The header above is an h3 element, which may be used for any form of page-level header which falls below the h2 header in a document hierarchy. More than one may be used per page.

Fourth-Level Header

For all headers below third-level, follow the guidelines listed above. Only use lower header levels when necessary.

Fifth-Level Header

For all headers below third-level, follow the guidelines listed above. Only use lower header levels when necessary.

Sixth-Level Header

For all headers below third-level, follow the guidelines listed above. Only use lower header levels when necessary.

Paragraphs

All paragraphs are wrapped in p tags. Additionally, p elements can be wrapped with a blockquote element if the p element is indeed a quote. Historically, blockquote has been used purely to force indents, but this is now achieved using CSS. Reserve blockquote for quotes. Here's an example of correct usage:

Additionally, you might wish to cite the source, as in the above example. (The correct method involves the cite attribute directly applied to the blockquote element, but since no browser makes any use of that information whatsoever, it's useful to also specify the standalone cite element.)

Inline Text

You might have noticed all the monospaced text in this guide. There are a number of inline HTML elements you may use anywhere within other elements, including abbr, acronym, cite, code, del, em, ins, kbd, strong, and var.

abbr

Used for any abbreviated text, whether it be acronym, initialism, or otherwise. Generally, it's less work and useful (enough) to mark up only the first occurence of any particular abbreviation on a page, and ignore the rest. Any text in the title attribute will appear when the user's mouse hovers the abbreviation (although notably, this does not work in Internet Explorer for Windows). Example abbreviations and usage: NASA, HTML, and Mass.

acronym

Used for only specific abbreviations. Like abbr, any text in the title attribute will appear when the user's mouse hovers the acronym (unlike abbr, however, this does work in Internet Explorer for Windows.) According to Mirriam Webster, acronyms are:

...a word (as NATO, radar [...] ) formed from the initial letter or letters of each of the successive parts or major parts of a compound term; also : an abbreviation (as FBI) formed from initial letters.

If you think the difference between acronym and abbr is esoteric, you're probably right.

code

Used for computer code samples. Useful for technology-oriented sites, not so useful otherwise. Example code and usage:

function getJello() {
echo $aDeliciousSnack;
}

Inline usage: just like elsewhere in this document, HTML elements like em or code can be considered code, and marked up as such.

cite

Used for defining a citation or reference to other information sources. Example cited text and usage: More information can be found in [ISO-0000]

del

Used for deleted or retracted text which still must remain on the page for some reason. Since the default style includes a strikethrough line, it's preferable to the s element. The del element also has a datetime attribute which allows you to include a timestamp directly in the element. Example deleted text and usage: She bought twofive pairs of shoes.

em

Used for denoting emphasized text. In most instances where you'd want to italicize text (using the HTML element i or otherwise) you should use the em element instead. Notable exceptions are stylistic italicizing of proper titles, foreign languages, etc. where italicizing is used for differentiation instead of emphasis. In those cases, no proper HTML elements exist, so an i element or a span element with a custom class may be preferable. Example emphasized text and usage: You simply must try the negitoro maki!

ins

Used for inserted text and counterpart to the del element. Like del, ins has a datetime attribute which allows you to include a timestamp directly in the element. Example inserted text and usage: She bought twofive pairs of shoes.

kbd

Used for text which should be typed by the user. Mainly useful for computer instructions. Example keyboard text and usage: Please press Enter to continue.

strong

Used for denoting stronger emphasis than the em element. In most instances where you'd want to bold text (using the HTML element b or otherwise) you should use the strong element instead. Notable exceptions are stylistic bolding of examples, first occurences of names in an article, etc. where bolding is used for differentiation instead of emphasis. In those cases, no proper HTML elements exist, so b element or a span element with a custom class may be preferable. Example strong text and usage: Don't stick nails in the electrical outlet.

var

Used for variables within computer code snippets. Useful for technology-oriented sites, not so useful otherwise. Example code and usage: Add 5 to $result and recalculate.

Lists

Then there are the lists. ul denotes an unordered list (ie. a list of loose items that don't require numbering, or a bulleted list). ol denotes an ordered list, and various numbering schemes are available through the CSS (including 1,2,3... a,b,c... i,ii,iii... and so on). Each item within the ul or ol requires a surrounding <li> and </li> tag, to denote individual items within the list (as you may have guessed, li stands for list item).

Additionally, dl is another list type called a definition list. Instead of list items, the content of a dl consists of dt (Definition Term) and dd (Definition description) pairs. Though it may be called a "definition list", dl can apply to other scenarios where a parent/child relationship is applicable. For example, it may be used for marking up dialogues, with each dt naming a speaker, and each dd containing his or her words.

Example lists and usage:

This is an unordered list.

It has two items.

This is an ordered list.

It has two items.

No, I lied, it has three.

This is a term.

This is the definition of that term, which both live in a dl.

Here is another term.

And it gets a definition too, which is this line.

Here is term that shares a definition with the term below.

Here is a defined term.

dt terms may stand on their own without an accompanying dd, but in that case they share descriptions with the next available dt. You may not have a dd without a parent dt.